1. Field of the Invention
This invention relates to apparatus for towing vehicles, such as wrecked automobiles and trucks, and other heavy loads that require towing. More particularly, this invention is directed to towing apparatus of the type that is mounted on a towing vehicle provided with means for elevating and supporting one end of the towed vehicle while the opposite end of the towed vehicle is supported by wheels rotating along the ground. This invention incorporates a thrust reversal system that enables the towing apparatus of this invention to be safer and more efficient than prior art apparatus.
2. Prior Art Problems and Proposed Solutions
It is desirable to operate towing vehicles capable of loading and unloading towed loads as rapidly and efficiently as possible while consuming a minimum amount of fuel for each tow load. Therefore, a need existed for greater use of light weight towing vehicles having less complicated structure than existed in the prior art.
In most instances, a hoisting apparatus is usually mounted on such vehicles to lift and support a vehicle being towed. Such hoisting apparatus included a lifting device that extends rearward beyond the rear end of the chassis of the towing vehicle.
Frequently, the towed load is so heavy that it causes a substantial counter balancing of the weight of the towing vehicle forwardly of its rear wheels. This counterbalancing force tends to lift the front wheels of the towing vehicle about an axis defined by its rear wheels. This front wheel lifting tendency makes it difficult to steer the towing vehicle and also makes it hazardous to drive said vehicle.
When a relatively light weight towing vehicle is coupled to a relatively heavy towed load, the traction forces between the front wheels mounted on a front wheel axle and the rear wheels, mounted as a pair on a rear axle or mounted in tandem on a pair of rear axles of the towing vehicle, become distributed in a rearward direction of the coupled bodies. The heavy weight load being towed tends to pivot the towing vehicle about its rear axis interconnecting its rear wheels, thereby lifting its front wheels off a road to cause the problems previously discussed.
The danger resulting from the tendency to lift the towing vehicle in the vicinity of its front wheels is increased when the coupled bodies are accelerated in the forward direction. Therefore, towing vehicles have been provided with sufficient initial weight at their front ends to counteract the forces that tend to lift the front end wheels of the towing vehicle. Previous arrangements to obtain this added rear axle pressure have required complicated devices housed in specially built vehicles and have increased the fuel consumption of the towing vehicles whenever they were moved, either with or without a load in tow.
It has been suggested to transmit the kinetic and potential energies of the towed load to the front of the towing vehicles by means of tension springs and articulated lever arrangements which convert horizontal tensile forces into vertical pressure forces. These suggested arrangements cannot be utilized properly unless further complicated mechanical contrivances such as semi-rigid mechanisms are included. These contrivances complicate the construction of the devices to control the kinetic and potential energies to such an extent that they are impractical because they are expensive to build and require frequent repair and considerable maintenance.
The following proposals to reduce the tendency of a heavy load to create a moment of force about a rear axis of a towing vehicle to lift its front wheels have been followed with results that require further improvement.
1. Increase the weight in the vicinity of the front axle of the towing vehicle. A drawback to this proposal is that it requires the towing vehicle to be so heavy that permanent increase of its fuel consumption results.
2. Make the wheel base of the towing vehicle as long as practicable. However, an excessive length of the towing vehicle impairs the ability of a driver to control the maneuverability of the towing vehicle.
3. Keep the overhang of the recovery crane hook extending rearwardly from the rear suspension or rear axle of the towing vehicle to a minimum. Such an arrangement complicated loading and unloading of a vehicle to be towed because it limits the access space between the towing vehicle and the towed vehicle.
4. Provide a towing vehicle with means for moving one or more longitudinally moving masses that are mounted for longitudinal movement along the length of the towing vehicle to vary the front axle loading of the vehicle in response to the different moments of force that are applied to a towing vehicle about a transverse axis of pivoting defined by the rear axis of the towing vehicle in response to different weights of the towed load. This latter suggestion requires permanently adding considerable mass to the towing vehicle. The added mass deleteriously affects the efficient operation of the towing vehicle because its great weight requires increased fuel consumption at all times.
The incorporation of any of the aforesaid proposed features or any combination of one or more of them has led to uneconomical and costly designs in prior attempts to provide an acceptable tow performance.
2. Prior Art Patents and Their Limitations
U.S. Pat. No. 2,111,341 to TETRAULT, issued Mar. 15, 1938, shows a towing vehicle 10 having a chassis 11 supporting a pivotable boom 20 on an auxiliary frame 19. Boom 20 pivots about a pivot shaft 23. The ends of shaft 23 extend through slots 46 formed in webs of side channels of the auxiliary frame 19. Rollers 48 and 49 are journaled on each end of shaft 23. Thus, pivotable boom 20 pivots downward to receive the front end of a load such as wheels of an automobile to be towed and shaft 23 moves forward along slots 46 of the towing vehicle as the boom 20 pivots to lift the front end of the towed vehicle. However, even in its forwardmost position, pivot shaft 23 is to the rear of the rear wheel 12 of the towing vehicle so that the load of the towed vehicle always causes a moment of force in a direction that tends to lift the front wheels of the towing vehicle thereby leaving unresolved the problems described hereinbefore.
U.S. Pat. No. 2,747,890 to GERHARDT et al., issued May 29, 1956, shows a coupling device for producing additional ground pressure of both coupled vehicles. Three modifications of coupling devices are shown to couple railroad cars, the wheels of which are constantly on a common set of tracks. In this patent, the lifting arrangement commonly used in a towing apparatus for lifting and towing a wrecked vehicle is not a problem that this patented invention faces.
U.S. Pat. No. 3,687,315 to DONALDSON, issued Aug. 29, 1972, shows a coupling between a towing truck 1 that supports a pivotable crane 10 that pivots about a transverse axis 14 substantially aligned in a vertical plane with the rear wheels 5 and 6 of the towing vehicle and connected to a towed vehicle 19 by a series of elements such as a pulley wheel, a suspension cable 17, a hook 18 at the end of the suspension cable 17, a compression member 20 and an adjustable chain link assembly 28 attaching compression member 20 to the front and rear of a casualty vehicle and actuating a hydraulic ram 21 to apply a tension in a wire rope assembly 25. This arrangement induces a compressive force in compression member 20. The attachment points of hydraulic ram 21 and compression member 20 on the rear end 13 of the towing vehicle and a cross member 22 of the chassis frame constitute a couple acting in opposition to the moment produced by loading a jig 11 with casualty vehicle 19 to the rear of the rear wheels 5 and 6 of the towing vehicle. The inclusion of an adjustable chain link assembly 28 between the towing vehicle 1 and the towed load 19 reduces the control for turning the assembly of towing vehicle and towed vehicle.
U.S. Pat. No. 4,265,463 to PERRUSO, issued May 5, 1981, shows a combination vehicle for towing, dumping and the like. An important feature of this device is a vertical boom 50 located to the rear of the pivot axis formed by the rear wheels 16 of the towing vehicle. Under these circumstances, the moment of force about the pivot axis along the rear wheel axle of the towing vehicle always acts in a direction that tends to lift the front end of the towing vehicle. The moment of force applied by the towed vehicle 48 is always applied in a downward direction to the rear of the rear axle of rear wheel 16 of the towing vehicle in this patent.
U.S. Pat. No. 4,318,657 to ZNIDARIC, issued Mar. 9, 1982, shows a loading and transporting vehicle to tow heavy objects. In this patent, a loading bridge 1 is mounted directly on the under carriage 2 of the towing vehicle. The loading bridge 1 pivots relative to under carriage 2 about a transverse axis 11 that is located slightly forward of a rear axle 13 about which its rear wheels 29 rotate. The major portion of the towed vehicle is usually supported to the rear of the rear axle 13 so that the effect of the moment of force due to the towed vehicle about rear wheel axle 13 of the towing vehicle is always in the direction that tends to lift the front wheel axle of the towing vehicle of this patent.
U.S. Pat. No. 4,664,585 to AMBRIDGE et al., issued May 12, 1987, mounts a pair of longitudinal tracks 16 on a bed 19 of a chassis 2 of a towing vehicle 1 and provides hydraulic rams 17 for slidably mounting a pair of masses 15 on the chassis 2 for longitudinal movements along tracks 16 to compensate for the reduced front axle loading that occurs when a towed vehicle carried by a lower section 13 extending rearward of a lifting beam 8 increases the moment of force applied behind pivot 9 of the towing vehicle which tends to lift front wheel axis 4 of the truck. The incorporation of heavy masses 15 needed to move the center of gravity of the system forward of the rear wheel axis makes it difficult to control steering of the towing vehicle and requires a large amount of fuel to operate, so that it is not fuel efficient.
U.S. Pat. No. 4,761,110 to BOUTILIER, issued Aug. 2, 1988, discloses a vehicle lifting and towing apparatus attached to an intermediate portion 12 of a rear bumper of a towing vehicle 10. Intermediate bumper portion 12 of the rear bumper is pivotally attached to a lifting frame 16. The latter is pivotally attached to a main frame 22 about a main pivot shaft 24 and also is provided with hydraulic actuators 48 that move a sub frame 42 of the lifting frame 16 in a direction longitudinally of the main frame 22 of vehicle 10. A spring 68 is mounted on a bracket 66 on each side of the vehicle between lifting frame 16 and a rear axle 70 for towing vehicle 10 to protect lifting frame 16 from excessive jarring. In this patent, lifting frame 16 is directly attached to main frame 22 of the towing device both forward and rearward of the rear wheel axle 70. Lifting frame 16 can be stored beneath main frame 22 when the vehicle is not used for towing.
A common drawback in all of the aforesaid prior art references is a direct attachment between an auxiliary frame that supports a lifting mechanism and the main frame of the towing vehicle behind or to the rear of a transverse axle which supports rear wheels about which the towing vehicle would tend to rotate. Hence, when the towing vehicle tows an excessive load, the prior art only provides heavy mass at or near the front end of the towing vehicle, which increases fuel consumption while counteracting front end lifting. Alternative prior art solutions require complicated connecting means between the towing vehicle and the towed vehicle. Such apparatus requires frequent repair and maintenance that are both expensive and time consuming.